Recently, tray sealing apparatuses have been used in restaurants such as, for example, take-out restaurants and fast-food restaurants or markets so as to provide a food such as, for example, a wet food or a friable food in a state where the food is packed in a disposable tray. When the food is hermetically sealed, the food may be kept for a long time without going bad due to air. The hermetically sealed food may be conveniently kept under refrigeration, and when enjoying outdoor activities, the hermetically sealed food may be conveniently carried and stored. Accordingly, home tray sealing apparatuses for home use have been released.
FIG. 1 is a perspective view illustrating a conventional tray sealing apparatus.
Referring to FIG. 1, the tray sealing apparatus includes: a seal film supply unit provided with a plurality of rollers 101 on which a thermoplastic seal film roll RO is laid; a base body 100 provided with a tray reception hole 103 where a disposable tray T may be inserted; a cover unit 200 pivotally coupled to the top surface of the base body 100; and a heating plate 300.
The heating plate 300 is typically formed of aluminum or stainless steel and provided with an electric heating element (not illustrated) on the rear surface thereof. When an electric power is applied to the electric heating element, heat is generated from the electric heating element and the heating plate is heated to a predetermined temperature (e.g., 160° C. to 180° C.) by the heat from the electric heating element. A cutter 201 is disposed on the bottom surface of the cover unit 200 at a position between the seal film supply unit and the tray reception cavity 102.
As for the seal film, a dry laminated film of a PET (polyethylene terephthalate) film and a PP (polypropylene) film is typically used. In addition, the disposable tray T is typically formed from the PP film or the PET film and provided with a peripheral rim around the opening thereof
When sealing the tray T, a user turns ON the tray sealing apparatus 10 and stands by until the heating plate 300 is heated to a predetermined temperature (e.g., 160° C. to 180° C.) by the electric heating element (not illustrated).
Then, the user inserts the tray T containing a food into the tray reception hole, and pulls the seal film from the seal film supply unit to cover the opening of the tray. Then, the cover unit 200 of the tray sealing apparatus 10 is closed, the seal film is cut in the state where the seal film covers the tray T, and the heating plate 300 mounted on the bottom surface of the cover unit 200 heats the seal film so that the seal film adheres by fusion to the peripheral rim of the tray T. Consequently, the food contained in the tray T is hermetically sealed not to contact with external air.
However, the above-described conventional tray sealing apparatus 10 includes several serious problems as follows.
First, in order to seal the tray with the seal film by fusion, the heating plate 300 should be heated to a temperature that is not lower than the melting point of the seal film. However, such heating requires a long time and a lot of energy. In addition, once heated, the heating plate retains latent heat for a long time without being quickly cooled even after the sealing is completed, thereby causing various problems as discussed below.
More specifically, the heating plate 300 typically provided in the food tray sealing apparatus has a large area and a relatively thick thickness so as to sufficiently cover the opening of a tray to be sealed and to support or incorporate the electric heating element and related components. For example, the heating plate employed in the conventional tray sealing apparatus available on the market usually has an area not less than 300 cm2 (15 cm×20 cm) and a thickness not less than 1 cm. In other words, the conventional heating plate has a relatively large volume.
The conventional tray sealing apparatus provided with such a heating plate with a large volume requires a long time and consumes a lot of power in order to heat the heating plate with the large volume to a temperature required for sealing a disposable tray with a seal film by fusion, for example, about 160° C. to 180° C. at the initial sealing stage.
In practice, the power consumed by existing food tray sealing apparatuses are usually in the range of about 550 W to 1,000 W, and an AC (alternating current) power source of 110V or 220V is used for sealing such food tray sealing apparatuses. When heating the heating plates configured as described above to a temperature in the range of 160° C. to 180° C. which is used for sealing a disposable tray at the initial sealing state using the electric power as described above, a long time not less than about 5 minutes may be required.
Accordingly, in an environment where sealing should be performed repeatedly at irregular time intervals (i.e., sometimes at long intervals and sometimes at short intervals), for example, in a restaurant, the heating plate should be kept in a preheated state so as to reduce the time required for heating the heating plate. Accordingly, even if the tray sealing apparatus is not used for a relatively long period of time, the power should remain turned ON. Accordingly, energy consumption is high. Further, since the high electric power as described above is used in order to rapidly heat the heating plate, the commercial AC power source of 110V or 220V is used as it is, which may cause an electric shock to the user.
A more serious problem in the existing food tray sealing apparatuses is that, due to the large volume of the heating plates as described above, high latent heat is retained in the heating plates for a long time even after the sealing is completed and thus, a considerable length of time is required to cool the heating plates. It has been known that, in order to naturally cool the heating plates to a temperature in the non-heated state, the existing food tray sealing apparatuses require a long time which is twice or more the time required for heating the heating plate to the temperature for adhesion by fusion due to the latent heat, which may cause serious problems as described below.
First, since the high latent heat is retained for a long time in the heating plate, it is highly probable that the user may get a burn when inadvertently touch the heating plate. When such a food tray sealing apparatus is repeatedly and continuously used, for example, in a restaurant, it is required to continuously and repeatedly heat the heating element in a state where the latent heat is retained. Accordingly, a portion or area around the heating plate in the tray sealing apparatus may be overheated.
In addition, during the sealing of a tray, the tray or the seal film may be widely and excessively heated to a portion other than a sealing target portion (the peripheral rim around the opening of the tray or a portion corresponding to the peripheral rim). As a result, the tray may be crumpled or distorted or the seal film may get stuck to the heating plate so that a mark of the heating plate may be left on the top surface of the seal film. Such a deformation may give a customer an unpleasant feeling and make it difficult to stack up trays for storage. Accordingly, it may be required to perform sealing again.
Further, when the overheated condition is continued or repeated, thermal stresses are continuously and cumulatively applied to various portions or areas in the food tray sealing apparatus other than the heating plate such as, for example, a body case including the base body and the cover unit. Accordingly, for example, when the body case is fabricated using a material vulnerable to heat, it may be deformed or damaged by the thermal stresses.
Thus, it may be difficult to employ a thermoplastic resin material which is excellent moldability and inexpensive such as, for example, an acrylonitrile butadiene styrene (ABS) resin as a material for the body case or the like in the tray sealing apparatus. In order to solve such a problem, a portion to be frequently heated may be made of a metallic material such as a stainless steel material. However, it may greatly increase the weight of the entire apparatus to make it difficult to move or handle the tray sealing apparatus, while increasing the manufacturing costs. Further, such a limitation in material remarkably degrades design flexibility for the exterior appearance of the tray sealing apparatus.
Meanwhile, the conventional tray sealing apparatus remains for a long time in a state where the heating element retains high latent heat even if the power is turned OFF after sealing. In addition, the temperature of the heating plate is fluctuated depending on the number of times of sealing or whether the time interval between sealing steps is long or short when the sealing is repeatedly performed. Thus, it is difficult to properly control the temperature of the heating plate. In other words, it is difficult to secure either a suitable sealing condition when sealing the tray with a seal film by fusion or a suitable cooling condition after sealing.
Accordingly, it is difficult to ensure a suitable sealing quality with the conventional tray sealing apparatus. For example, the seal film may be excessively molten so that a suitable sealing effect may not be obtained. Also, since the heating plate is cooled slowly due to the latent heat, after sealing, the heating plate may be separated from the seal film in a state where the surface of the seal film in the sealed area is not sufficiently cured and thus, is somewhat sticky. Thus, the sealed surface of the seal film is hardly formed smoothly.
In order to solve these problems, the tray sealing apparatus may be provided with a means for controlling the temperature of the heating plate (or an electric heating element for heating the heating plate) based on the temperature of the heating plate, the heating cycle, and the cumulative number of times of sealing. However, even in an environment where the tray sealing apparatus is frequently used like a fast-food store, it is inevitable that sealing is performed at irregular intervals. Accordingly, since the level of latent heat remaining in the heating plate and the temperature of the heating plate or the surroundings thereof are varied depending on the number of times of sealing and time intervals, there are a lot of parameters to be monitored and analyzed in order to suitably control the sealing temperature and time. Accordingly, it is very difficult to prepare a means for precisely controlling the sealing condition and the cooling condition after sealing and considerable costs may be additionally required for preparing such a control means.
For example, food tray packaging apparatuses of the type as described above are disclosed in Korean Utility Model Registered No. 20-3041719 filed on Nov. 27, 2003 as Utility Model Application No. 2003-0037004 and registered on Feb. 14, 2004 in the name of Enterline Co. Ltd. (“Enterline”) and Korean Patent Laid-Open Publication No. 2009-0075582 filed on Jan. 4, 2008 as Korean Patent Application No. 2008-0001497 and published on Jul. 8, 2009 in the name of GMPS Co. Ltd. (“GMPS”).
Enterline includes a heating plate which is provided with a plurality of electric heating elements on the top surface thereof. An opening is formed through the central area of the heating plate and several components such as, for example, a bearing are disposed in the opening. In addition, Enterline includes an elastically flexible silicon rubber mounted on a tray abutment and configured to absorb impact applied to the tray abutment by the heating plate at the time of sealing.
However, the opening formed in the central area of the heating plate in Enterline is provided in order to secure a space for disposing several components such as the bearing, rather than in consideration of the reduction of the heating time of the heating plate.
Enterline is made to solve the problem caused as impact is applied to the tray abutment by the heating plate in which Enterline also considers the strength of the heating plate as an important factor. In other words, Enterline apparatus does not consider various problems such as, for example, a long heating time, high power consumption, and high latent heat of the heating plate in providing the opening. The bearing or the like disposed in the central opening may disturb the release of the latent heat from the heating plate.
Further, the heating plate of Enterline should have a thickness sufficient for securing a strength required in spite of providing the opening therein. Accordingly, it can be seen that Enterline also includes various problems including a significant length of time required for heating the heating plate to a predetermined temperature, high power consumption, and the delayed cooling of the heating plate due to the large volume of the heating plate.
Meanwhile, the objects of GMPS are to reduce power consumption and to suppress a user from suffering burns using a ruthenox electric heating element which is an instantaneous heating element. The ruthenox electric heating element is well-known in the related technical field and configured to enable instantaneous heating by applying a high electric power within a short time.
GMPS is configured such that plural ruthenox electric heating elements are set on the rear surface of a wide heating plate to be suitable for the sizes of various kinds of trays, respectively, and when performing sealing, one of the electric heating elements which has a size corresponding to that of a tray to be sealed may be turned ON through a selection switch.
However, in order to heat the various kinds of trays from a small tray to a large tray, it is necessary to use a wide heating plate. In addition, the heating plate should have a sufficient strength and rigidity to retain the bottom surface of the heating plate to be flat consistently. Consequently, it is inevitable that the heating plate should also be thick.
Further, in order to heat the heating plate set with the ruthenox electric heating elements as described above to a melting point of a seal film, for example, to a temperature in the range of 160° C. to 180° C. within a short time, very high electric power, for example, 1,500 W to 1,800 W, and hence a very high voltage should be applied instantaneously to a corresponding ruthenox electric heating element, which may cause a user to get a serious electric shock.
Even if the heating plate may be quickly heated by the high instantaneous voltage, after sealing, the heating plate retains latent heat for a considerable length of time without being rapidly cooled due to the wide area and thick thickness, i.e., the large volume of the heating plate. In other words, also in the case of GMPS apparatus, latent heat is retained in the heating plate for a long time after the sealing is completed and when the sealing is repeatedly performed with short time intervals, the heating plate continuously remains at a high temperature.
Accordingly, GMPS also includes most of the problems caused in Enterline as the latent heat remains for a long time in the heating plate.
That is, due to the delayed cooling of the heating plate, the user may suffer burns, sealed trays may be overheated and deformed when sealing is continuously performed, and sealed surfaces may not be formed smoothly. In addition, since the components around the heating plate may also be overheated and deformed, there is a limit in material used for fabricating the constitutional components, design flexibility for the external appearance is degraded, and a proper control of sealing conditions is difficult. It is highly probable that GMPS may cause a serious electric shock due to the instantaneous heating of the heating plate.